Q> Как определить,принадлежит ли юзер группе администраторов?
A> Два метода в одном флаконе:

#include <windows.h>
#include <stdio.h>
#include <lm.h>
#pragma hdrstop

#pragma comment( lib, "netapi32.lib" )

// My thanks to Jerry Coffin (jcoffin@taeus.com)
// for this much simpler method.
bool jerry_coffin_method()
{
bool result;
DWORD rc;
wchar_t user_name[256];
USER_INFO_1 *info;
DWORD size = sizeof( user_name );

GetUserNameW( user_name, &size);

rc = NetUserGetInfo( NULL, user_name, 1, (byte **) &info );
if ( rc != NERR_Success )
return false;

result = info->usri1_priv == USER_PRIV_ADMIN;

NetApiBufferFree( info );
return result;
}


bool look_at_token_method()
{
int found;
DWORD i, l;
HANDLE hTok;
PSID pAdminSid;
SID_IDENTIFIER_AUTHORITY ntAuth = SECURITY_NT_AUTHORITY;

byte rawGroupList[4096];
TOKEN_GROUPS& groupList = *( (TOKEN_GROUPS *) rawGroupList );

if ( ! OpenThreadToken( GetCurrentThread(), TOKEN_QUERY, FALSE, &hTok ) )
{
printf( "Cannot open thread token, trying process token [%lu].\n",
GetLastError() );
if ( ! OpenProcessToken( GetCurrentProcess(), TOKEN_QUERY, &hTok ) )
{
printf( "Cannot open process token, quitting [%lu].\n",
GetLastError() );
return 1;
}
}

// normally, I should get the size of the group list first, but ...
l = sizeof rawGroupList;
if ( ! GetTokenInformation( hTok, TokenGroups, &groupList, l, &l ) )
{
printf( "Cannot get group list from token [%lu].\n",
GetLastError() );
return 1;
}

// here, we cobble up a SID for the Administrators group, to compare to.
if ( ! AllocateAndInitializeSid( &ntAuth, 2, SECURITY_BUILTIN_DOMAIN_RID,
DOMAIN_ALIAS_RID_ADMINS, 0, 0, 0, 0, 0, 0, &pAdminSid ) )
{
printf( "Cannot create SID for Administrators [%lu].\n",
GetLastError() );
return 1;
}

// now, loop through groups in token and compare
found = 0;
for ( i = 0; i < groupList.GroupCount; ++ i )
{
if ( EqualSid( pAdminSid, groupList.Groups[i].Sid ) )
{
found = 1;
break;
}
}

FreeSid( pAdminSid );
CloseHandle( hTok );
return !!found;
}

int main()
{
bool j, l;

j = jerry_coffin_method();
l = look_at_token_method();

printf( "NetUserGetInfo(): The current user is %san Administrator.\n",
j? "": "not " );
printf( "Process token: The current user is %sa member of the Administrators
group.\n",
l? "": "not " );

return 0;
}